As the luminous efficiency of the light-emitting diode (LED) has been increasing, the extent of the LED applications has become broader and broader, ranging from the traditional indication, lighting sources to various sorts of backlight sources, such as portable flashlights, backlights of mobile phones or liquid crystal displays (LCDs).
Many researches have been widely involved in the development of white light LEDs as LCD backlight sources in order to replace cold cathode fluorescent lamps (CCFL) that have been traditionally used as light sources. One of the related methods is to uniformly mix the light emitted respectively by the red, green, blue LEDs, which are disposed properly, and thereby to produce white light. FIG. 1 shows the light-emitting device disclosed by West et al. in U.S. Pat. No. 6,974,229, capable of improving the light-mixing efficiency of the neighboring red, green, and blue LEDs. The light-emitting device 10 comprises an optical lens 12, and the form of the optical lens 12 is customized so as to redirect light to the lateral regions 13 for enhancing the light extraction efficiency in horizontal directions such that the light-mixing efficiency with neighboring LEDs is improved. FIG. 2 shows the light-emitting device disclosed by Park et al. in US2006/0001034 for improving light-mixing efficiency. A light-emitting device 20 comprises a red, green, and blue LED, a resin 24 encapsulating the LEDs, and light-mixing materials 23 dispersed uniformly within the resin 24. The light-mixing materials 23 are served to scatter light emitted from the LEDs randomly such that the light-mixing efficiency with neighboring LEDs can be improved.
The above-mentioned methods emphasize on providing a light-mixing mechanism upon the LEDs for reducing the light-mixing distance. However, the design of a customized optical lens or the fabrication process including encapsulating the light-mixing materials with a resin is complicated. Besides, the cost is increased as well.